A lamp for motor vehicles typically contains multiple lighting units, wherein each of these lighting units provides a different light function or contributes to ensuring the required emission characteristic of the light trace. Individual lighting units are generally mounted in a shaped carrier housing, while each unit comprises at least one light source and other optical elements. The light source emits light rays and the optical elements represent a system of refractive and reflective surfaces and interfaces of optical environments that influence the direction of light rays within the creation of the output light trace.
Currently, a homogeneous or interesting appearance from the designer point of view is emphasized in the context of ensuring the light functions in light devices designed for motor vehicles, namely both during active lighting and in the off state. E.g. the document EP2390137 discloses a design wherein a three-dimensional appearance of the output light trace is achieved by a mirror tunnel in the lit up state, the appearance being produced by a multiple reflection of light rays between two mirror surfaces, the front mirror surface being semi-permeable and permitting a part of the light beam in the direction of the optical axis X. The use of a semi-permeable mirror is also known from the document US20150062946A1, where an organic electroluminescence diode of the OLED type is fitted with a semi-permeable mirror surface on its inner side. A part of the light rays passes through the OLED out of the light device, and a part of the light rays is directed into the inner space of the light device onto a mirror surface, which produces a multiple reflection in the form of a tunnel effect. A disadvantage of the above-mentioned designs is very low efficiency of the optical assembly, while a black appearance of the lamp in the off state is not possible as, e.g., in the case of mobile phones where after switching the backlight off the phone display is black with a mirror reflection on its external surface.
In the prior art, a great number of designs can be found that enable darkening of a light-emitting surface. E.g., the document EP0399506 discloses the use of the properties of special electrically controlled polymer dispersed liquid crystal (PDLC) films. A disadvantage of this design is the fact that the film is placed between two carrier plates, and such an arrangement restricts the spatial shape of the light emitting surface. In addition, the film is controlled by alternating voltage with the need of using a special power supply/inverter. Another disadvantage is the time required for switching from the transparent active state to the opaque inactive state. This time is relatively long with respect to the requirement to light up, e.g., the Stop function almost immediately. Using the SPD glass technology is also known from the prior art, which makes it possible to control the amount of light penetrating through a glass light-emitting surface during a short time period. Solutions using PDLC film or SPD glass known so far are also characterized by high production complexity and limited applicability in serial production in the art of the lighting technology of motor vehicles. The technology of hot plastic injection molding is commonly used in the art of lighting devices and the use of PDLC or SPD glass is demanding from the technological, design and financial point of view.
Another prior art solution consists in using an LCD display, described e.g. in the document WO 2016025982 A1. Again, its disadvantage is that this element requires active control by means of further electronic control devices as well as costly production if the display should follow the shape of the surface of the covering glass of the lamp.